1. Field of the Invention
The present invention relates to an azobenzene derivative capable of emitting stable fluorescence for an extended period by forming an aggregate, a fluorescent particle formed by aggregates of the azobenzene derivative, and a method of fabricating the fluorescent particle.
2. Discussion of the Background
Numerous organic chromophores and polymers have been proposed as fluorescent materials in recent years (see R. H. Friend, et al. Nature 1999, 397, 121; R. Jakubiak, et al. J. Phys. Chem. A 1999, 103, 2394; H. Murata, et al. Appl. Phys. Lett. 2002, 80, 189., which are expressly incorporated herein by reference in their entirety). However, although these fluorescent materials produce strong fluorescence in dilute solutions, there is a problem in that the intensity of fluorescence decreases in the solid state due to the formation of aggregates. It is difficult to achieve high-intensity fluorescence with such fluorescent materials when fabricating them into thin film devices.
By contrast, the present inventors have discovered a novel benzene derivative that emits almost no fluorescence before aggregation, but emits fluorescence of much greater intensity once aggregated (Japanese Unexamined Patent Publication (KOKAI) No. 2006-160715, referred to as “Reference 1” hereinafter, or English language family member US 2006/194771 A1, which are expressly incorporated herein by reference in their entirety).
When irradiation with ultraviolet light is continued after inducing isomerization from the trans form to the cis form by irradiation with ultraviolet light, the azobenzene derivative described in Reference 1 aggregates by self-organization, forming an aggregate that emits intense fluorescence.
When irradiation with ultraviolet light is halted and the aggregate is placed at room temperature in a dark location, isomerization from the cis form to the trans form takes place within the aggregate of the above azobenzene derivative, thereby permitting emission of even greater intensity. However, depending on the application, it is sometimes desirable to maintain a stable absorption spectrum or fluorescence of constant intensity following formation of the aggregate.